1. Field of the Invention
The present invention relates to an image pickup apparatus and, more specifically, to an image pickup apparatus that can acquire image data for obtaining a high dynamic range image.
2. Description of the Related Art
A technique is known for combining plural images in different exposure times (e.g., two images in a short exposure and a long exposure) to obtain an image in a wide dynamic range exceeding a dynamic range obtained only with one image (a high dynamic range image).
An example of such a technique is explained with reference to FIGS. 26 to 28, FIG. 26 is a diagram showing an example of a configuration of a conventional image pickup section. FIG. 27 is a circuit diagram showing a configuration of one pixel in the conventional image pickup section. FIG. 28 is a timing chart showing a state in which a long exposure image and a short exposure image are alternately acquired frame by frame by the conventional image pickup section.
A conventional image pickup section 91 shown in FIG. 26 includes a pixel section 92 in which plural pixels are arrayed two-dimensionally (e.g., in a row direction and a column direction), a readout section 93 that reads out a pixel value from the pixel section 92 in a row unit and performs correlated double sampling with a CDS section and amplifying the pixel value with a gain section, and a digital processing section 94 that reads out a pixel value from the readout section 93 in a row unit and converts the pixel value into a digital signal.
As shown in FIG. 27, the pixel included in the pixel section 92 includes a PD (photodiode), which is a photoelectric conversion section, and an FD (floating diffusion), which is a signal accumulating section, that temporarily stores a signal of the photoelectric conversion section PD at the time of charge readout.
A transfer transistor TX for transferring the signal of the photoelectric conversion section PD to the signal accumulating section FD is connected in series between the photoelectric conversion section PD and the signal accumulating section FD.
TrA represents an amplification transistor functioning as an amplifying section. The amplification transistor TrA, a voltage source Vdd, and a current source configure a source follower amplifier. A signal of the signal accumulating section FD is amplified by the amplification transistor TrA and outputted to a vertical transfer line via a selection transistor to which a selection pulse is applied.
FDRST represents an FD reset transistor for resetting the signal accumulating section FD and an input section of the amplification transistor TrA. The FD reset transistor FDRST and the transfer transistor TX are simultaneously turned on, whereby reset of the photoelectric conversion section PD can also be simultaneously performed.
FIG. 28 shows a state in which a long exposure image and a short exposure image are alternately acquired frame by frame by the image pickup section having such a configuration.
For example, the image pickup section 91 performs readout of exposure data in a long exposure time TexpL in a certain frame. Exposure is a rolling shutter type. The image pickup section 91 resets the PD to set a long exposure time prior to readout timing. Thereafter, the image pickup section 91 sequentially performs readout of data from the pixel section 92 in a row unit at a rising edge of a vertical synchronization signal VD. The exposure is sequentially completed in a row unit simultaneously with the readout in the row unit. Consequently, a data output L related to long exposure is obtained from the image pickup section 91.
In the next frame, the image pickup section 91 performs readout of exposure data in a short exposure time TexpS. The image pickup section 91 sequentially performs readout of data from the pixel section 92 in a row unit at timing of a rising edge of the vertical synchronization signal VD. A data output S related to the short exposure is obtained from the image pickup section 91.
By repeatedly performing such processing, a long exposure image and a short exposure image are alternately acquired frame by frame. Therefore, a long exposure image obtained in a first frame and a short exposure image obtained in a second frame are subjected to high dynamic range combination, whereby a high dynamic range image for one frame is generated. Similarly, a long exposure image obtained in a third frame and a short exposure image obtained in a fourth frame are subjected to high dynamic range combination, whereby a high dynamic range image for the next one frame is generated. In this way, conventionally, a high dynamic range image at a half frame rate of an image pickup frame rate is acquired.
In the related art of this type, to obtain images in different exposure times, it is necessary to repeat photographing at different exposure timings plural times. Therefore, when a subject is a moving object, positional deviation occurs in the moving object in images exposed at the different timings.
As a technique for coping with such a point, for example, Japanese Patent Application Laid-Open Publication No. 2011-4353 describes an image processing apparatus that specifies common regions in images in different exposure times, calculates a positional deviation correction amount for causing the common regions to coincide with each other, and performs image processing.
In the technique described in Japanese Patent Application Laid-Open Publication No. 2011-4353, in order to perform positional deviation correction, a sophisticated image processing technique such as affine conversion or block matching is necessary. Therefore, it is necessary to perform processing in a computer separate from a camera or provide a sufficient processing function in the camera.
In the related art explained above, for example, when two images are combined, it is necessary to read out two images in order to obtain one combined image. Therefore, if it is attempted to obtain a high dynamic range image in a moving image, for example, when two images are combined, a frame rate is reduced to a half.